Halosilane chemicals find many uses in industry. In particular, iodosilane precursors, such as diiodosilane (SiH2I2), are used to deposit a variety of silicon containing films for use in semiconductor manufacturing processes.
Emeléus et al., disclose synthesis of diiodosilane (SiH2I2) by reaction of Silane (SiH4), Hydrogen Iodide (HI), and aluminum iodide (AlI3). Derivatives of monosilane. Part II. The Iodo compounds: Emeleus, H. J.; Maddock, A. G.; Reid, C., J. Chem. Soc. 1941, 353-358). The reaction produces the desired SiH2I2 reaction product along with Iodosilane (SiH3I), Triiodosilane (SiHI3), and tetraiodosilane (SiI4). Id. at p. 354.
Keinan et al. disclose the reaction of iodine and phenylsilane in a 1:1 molar ratio in the presence of traces of ethyl acetate at −20° C. produces 1 mol of SiH2I2 and 1 mol of benzene. J. Org. Chem., Vol. 52, No. 22, 1987, pp. 4846-4851. Although selective for SiH2I2 over the other possible iodosilanes (i.e., SiH3I, SiHI3, and SiI4), this method produces the known human carcinogen benzene, which makes commercial implementation difficult. Despite this drawback, it remains the preferred synthetic approach to producing Diiodosilane.
Impurities from these synthesis processes, such as hydrogen iodide and/or iodine, may decompose the resulting iodosilane product. Current industrial practice is to stabilize these products using antimony, silver, or copper powder/pellet additives as taught in Eaborn, ‘Organosilicon Compounds. Part II. ‘A Conversion Series for Organosilicon Halides, Pseudohalides, and Sulphides’, 1950, J. Chem. Soc., 3077-3089 and Beilstein 4, IV, 4009. Although the addition of copper may stabilize the product, it also may introduce impurities (Cu) which may adversely affect the electrical properties of the deposited films.
The so-called Finkelstein reaction is an SN2 reaction (Substitution Nucleophilic Bimolecular reaction) that involves the exchange of one halogen atom for another. Halide exchange is an equilibrium reaction, but the reaction can be driven to completion by exploiting the differential solubility of halide salts, or by using a large excess of the halide salt. Smith et al., (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience.
For example, the preparation of trimethylsilyl iodide (TMS-I) via reactions of trimethylsilyl chloride and lithium iodide in chloroform or sodium iodide in acetonitrile has been reported (Eq. 4). Handbook of Reagents for Organic Synthesis, Reagents for Silicon-Mediated Organic Synthesis, Iodotrimethylsilane, Wiley 2011, p. 325

While Si—Cl is reactive to iodine exchange by this route, R groups like alkyl or aryl groups are not. On the other hand, Si—H bonds are found in general to be more reactive than the Si—Cl bond. Chemistry and Technology of Silicones, Academic Press, 1968, p. 50. As a result, one of ordinary skill in the art would expect exchange of both the H and Cl atoms of any Si—H containing halosilane in the Finkelstein reaction.
A need remains for commercially viable synthesis and supply of stable Si—H containing iodosilanes, such as diiodosilane, suitable for use in the semiconductor industry.